Transmissions of signals for television generally occur over the air, over cable lines, or using satellite transmissions. These signals have a carrier frequency on which the video and audio data are carried. A suitable set-top terminal may be employed to receive any of these, by demodulating the carrier frequency to reconstruct the video and audio data. In particular, the set-top terminal includes a tuner that has a decoder with an adjustable narrow band pass filter, and the filter passes the signals of a selected channel to a video decoder.
A set-top terminal receives these signals when a user attaches one or more cables carrying these signals into the same. However, the set-top terminal does not know a priori what type and format of signal is being propagated by the attached cable. And if multiple jacks are provided on the set-top terminal to accommodate multiple types of signals, a user can easily attach the cables incorrectly, e.g., a user can inadvertently attach a cable carrying one type of a signal to a jack intended for a different type of signal.
The signal carried on a cable may be in one of several standardized formats, denoted cable channel identification standards: one is the “standard frequencies” standard (STD); a second is the “harmonic related carriers” standard (HRC); and a third is the “incremental related carriers” standard (IRC). Cable companies generally use one of these three standards, and set-top terminals provided by cable companies are usually programmed to the standard set by that company. However, it is common now for a consumer to be able to receive cable broadcasts from a number of cable companies, and each may employ a different standard. Moreover, it is common for consumers to purchase set-top terminals of their own, e.g., ones with digital video recording capabilities, and these are generally not hard-coded to a given cable company's standard. Even more, many set-top terminals may also receive off-air signals, and thus are required to be able to decode those signals as well.
To identify the signals carried by an attached coax cable, a scan is required to be made of the cable. However, conducting cable scans to detect signals over all possible channel frequencies and modulations is time-consuming given the large number of channels to scan, as well as the different standards. Accordingly, there is a need for an optimized method to rapidly detect ones of multiple types of signals that may be present on a signal-carrying cable.